System and method for assisting in rotor speed control

ABSTRACT

A method of assisting in rotor speed control in a rotorcraft can include measuring a rotor speed with a sensor; detecting a droop in the rotor speed beyond a lower droop limit; and commanding a decrease in collective in response to the rotor speed drooping beyond the lower droop limit. A system of assisting in rotor speed control in a rotorcraft, the system can include: a computer having a control law, the control law operable to generate a decrease collective command to an actuator in response to a rotor speed decreasing below a lower droop limit; wherein the lower droop limit is below a normal lower rotor speed range.

CROSS-REFERENCE TO RELATED APPLICATIONS Technical Field

This application claims priority to and is a continuation patentapplication of U.S. patent application Ser. No. 14/297,136, filed Jun.5, 2014, which claims priority to U.S. provisional application No.61/832,186, filed Jun. 7, 2013, all of which are hereby incorporated byreference for all purposes as if fully set forth herein.

BACKGROUND Technical Field

The present disclosure relates to a system and method of assisting inrotor speed control. More specifically, the system and method providesrotor speed control during rotor speed excursions outside of a normalrotor speed envelope.

Description of Related Art

Conventionally, certain rotorcraft have employed some level of rotorspeed control in a fly by wire flight control system. For example, rotorspeed can be controlled by an engine control unit. However, controllingrotor speed with the engine control unit has shortcomings in certainsituations.

There is a need for an improved flight control system.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the system and method ofthe present disclosure are set forth in the appended claims. However,the system and method itself, as well as a preferred mode of use, andfurther objectives and advantages thereof, will best be understood byreference to the following detailed description when read in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a side view of an rotorcraft, according to one exampleembodiment;

FIG. 2 is a partially schematic view of rotorcraft systems, according toone example embodiment;

FIG. 3 is a schematic view of a system, according to one exampleembodiment;

FIG. 4 is a schematic view of a droop protection loop, according to oneexample embodiment;

FIG. 5 is a schematic view of a method, according to one exampleembodiment; and

FIG. 6 is a schematic view of a computer system, according to oneexample embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the system and method of the presentdisclosure are described below. In the interest of clarity, all featuresof an actual implementation may not be described in this specification.It will of course be appreciated that in the development of any suchactual embodiment, numerous implementation-specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present disclosure, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the device described herein may beoriented in any desired direction.

The method and system of the present disclosure can provide rotor speedenvelope protection against several types of failures, or degradedoperation. One benefit is after a dual engine failure; however, it willalso provide envelope protection functionality during a full authoritydigital engine control (FADEC) failure, aggressive rotorcraft pitch-overmaneuvers, aggressive pitch-up maneuvers with high torque, and rapidcollective inputs, for example. The system is configured such that itdetects that a rotor excursion is too great, and it adjusts collectiveto maintain rotor speed within desired limits. The system is enabledduring normal operation and does not depend on detecting a dual enginefailure. Moreover, one benefit of the system and method is thatdetection of an engine failure is not required. Certain rotor systemscan dangerously and quickly lose rotor speed prior to a detection of anengine failure, therefore, the system and method of the presentdisclosure provide safety by detecting the loss in rotor speed andtemporarily reducing or eliminating rotor speed control responsible froman engine control unit to a collective control until the rotor speed isback within a normal rotor speed envelope.

Referring now to FIG. 1 in the drawings, a rotorcraft 101 isillustrated. Rotorcraft 101 can include a rotor system 103 with aplurality of rotor blades 105. The pitch of each rotor blade 105 can bemanaged in order to selectively control direction, thrust, and lift ofrotorcraft 101. For example, a swashplate mechanism 123 can be used tocollectively and/or cyclically change the pitch of rotor blades 105. Itshould be appreciated that swashplate mechanism 123 is merely exemplaryof one possible system for selectively controlling the pitch of rotorblades 105; for example, an independent blade control system is anotherexemplary system for selectively controlling the pitch of rotor blades105. Rotorcraft 101 can include an airframe 107, anti-torque system 109,and an empennage 111. Torque can be supplied to rotor system 103 andanti-torque system 109 with at least one engine 113. A main rotorgearbox 115 is operably associated with an engine main output driveshaft121 and the main rotor mast.

Rotorcraft 101 is merely illustrative of the wide variety of aircraftand vehicles that are particularly well suited to take advantage of themethod and system of the present disclosure. It should be appreciatedthat other aircraft can also utilize the method and system of thepresent disclosure.

A rotorcraft with a low inertia rotor system may especially benefit fromthe system and method of the present disclosure.

Referring now also to FIG. 2 in the drawings, a system 201 isillustrated in conjunction with rotorcraft 101. It should be appreciatedthat though system 201 is illustrated with regard to rotorcraft 101,system 201 is also implementable on other aircraft as well. Further, itshould be appreciated that system 201 can be implemented in a widevariety of configurations, depending in part on the flight controlconfiguration of the aircraft.

System 201 is particularly well suited for implementation in aircrafthaving a fly-by-wire flight control computer, such as flight controlcomputer 125; however, a partial fly-by-wire aircraft can also utilizesystem 201. For example, system 201 can be utilized with a flightcontrol system having collective actuators 124 a, 124 b, and 124 c thatcan receive commands from a trim motor, autopilot system, or any othersystem that allows collective commands to be realized by collectiveactuators 124 a, 124 b, and 124 c. Further, system 201 is particularlywell suited for implementation with aircraft having an engine controlledby an engine control unit 127, such as a FADEC (full authority digitalengine control) system. However, system 201 can also be implemented onan aircraft having an engine that is not controlled by an engine controlunit 127, in such an embodiment, system 201 can make fuel controlcommands directly to a fuel control unit 129, for example.

Referring now also to FIG. 3, a schematic view of system 201 isschematically illustrated in conjunction with features of rotorcraft101. System 201 is configured as an interface between engine 113,airframe 107, flight control computer 125, and collective actuators 124a-124 c. The flight control computer 125 uses data from the engine 113and rotor system 103 to calculate a collective pitch command. Any numberand variety of sensors can be utilized to provide certain data to flightcontrol computer 125 and system 201. System 201 is preferably integratedwith flight control computer 125; however, in another embodiment system201 can be a standalone computer system within the aircraft. Asdiscussed further herein, flight control computer 125 and system 201 caninclude computer related equipment, such as processors and the like forperforming associated functions.

Still referring to FIG. 3, system 201 can include control laws, whichare illustrated as vertical loops 205. Vertical loops 205 can includevertical axis control laws configured to make control commands so thatthe rotorcraft can hold a desired vertical axis state, such as verticalspeed or vertical altitude, for example. For example, the vertical loops205 can adjust for differences between a commanded vertical state and anactual vertical state. One example can be if rotorcraft 101 is directedto hold a commanded altitude, but rotorcraft 101 experiences a suddenupdraft of wind, then the vertical loops 205 can in response generatecommands to collective actuators 124 a-124 c in order to decrease pitchand thrust in order to maintain the commanded altitude.

System 201 can also include a controller 207 configured to adjust areceived command to minimize an error signal and then send outputadjusted commands to collective actuators 124 a-124 c. In oneembodiment, controller 207 includes a proportional plus integral (P+I)functionality; however, it should be appreciated that controller 207 mayinclude any implementation specific desired functionality.

One unique feature of system 201 is the inclusion of a droop protectionloop 203. Droop protection loop 203 is configured to detect a drop inrotor speed beyond a droop rotor speed limit (i.e. 7% below commanded).The droop rotor speed limit is set below a lower normal rotor speedrange (i.e. 3% below commanded) that may occur during normal maneuvers,and then make a decrease collective command to collective actuators 124a-124 c in order to quickly increase rotor speed. The rotorcraft 101will experience a nonpilot commanded decrease in altitude, but this isbetter than continuing to lose valuable rotor speed. One embodiment ofdroop protection loop 203 is described in FIG. 4, as discussed furtherherein. During normal operation, rotor speed is regulated by an enginecontrol unit of engine 113; moreover, if the pilot were to increasecollective pitch, the rotors would naturally tend to slow down due tothe increase in aerodynamic resistance; however, the engine control unitwould sense or anticipate such an affect and increase fuel to the engineto increase engine power and engine speed. Therefore, the collectivecommands from droop protection loop 203 are only realized when the droopprotection loop 203 generates decrease collective commands that are lessthan the decrease collective commands make by vertical loops 205. Aselector 209 can be configured to choose the lesser of the decreasepitch commands made by vertical loops 205 and droop protection loop 203.The commands generated by droop protection loop 203 can be output tocontroller 207 and then to a switch 211. Switch 211 is configured tocommunicate commands from controller 207 by default; however, switch 211will instead communicate commands from all engines inoperative (AEI)control laws 213 upon the detection of engine failure, or otherimplementation specific criteria. Thus, if a rapid drop in rotor speedis sensed, but the engine failure is not yet detected, then droopactivation loop 203 will function to send decrease collective commandsto collective actuators 124 a-124 c only until switch 211 turnsauthority over to AEI control laws 213, such as after detection ofengine failure. AEI control laws 213 can include autorotation controllaws that will assist in the autorotation and safe landing of therotorcraft 101. It should be appreciated that in such a scenario, droopactivation loop 203 will function to provide the important function ofpreserving rotor speed so that a more effective autorotation can beperformed with the assistance of AEI control laws 213. It should beappreciated that AEI control laws 213 are configured so that the pilotcan have the ability to directly control the collective pitch in orderto deliberately cause the rotor speed to decay during the autorotationflare and landing without activation of droop protection loop 203.

One challenge of a rotorcraft, such as rotorcraft 101, with a lowinertia rotor system 103, is an immediate and large compensation isrequired to control rotor speed after a dual engine failure. Pilotreaction time may not be sufficient to prevent excessive rotor speeddecay. For many types of engine failures, the engine failure will not bedetected until the rotor has already drooped significantly orexcessively. One advantage is that system 201 provides immediatecompensation with a large authority/bandwidth (faster than the pilot)and does not depend on detection of an engine failure.

System 201 is configured to selectively activate the droop protectionloop 203 which reduces collective rotor blade pitch based upon rotorspeed decay. The droop protection loop 203 is configured such thatcollective input commands will not be made during normal rotor speedexcursions, but rather after a decrease in rotor speed beyond a lowerrotor speed limit that is well beyond normal rotor speed excursions, butbefore an excessive reduction in rotor speed. In one illustrativeembodiment, droop protection loop 203 can be activated when rotor speeddecreases below a droop rotor speed limit, such as 5% below commandedrotor speed, to name one example. The activation conditions can be afunction of commanded rotor speed and/or other aircraft conditions (suchas to allow greater rotor speed droop at low altitude, for example).Moreover, system 201 can be configured to adjust the droop rotor speedlimit lower at high altitude (such as 10% of commanded, for example) andadjust the droop rotor speed limit higher (such as 5% of commanded, forexample) at low altitude.

In one example embodiment, system 201 can be configured with anoverspeed protection loop in order to prevent the rotor speed frompossibly overspeeding due to inflow dynamics. Due to the slowertransients, the overspeed protection can be lower bandwidth and lowerauthority.

Referring now also to FIG. 4, one embodiment of droop protection loop203 is illustrated in further detail. Values associated with a commandedrotor speed 401 and an actual rotor speed 403 are correlated with valuesin table 405. The table 405 provides flexibility over a standardlinear/gain system, in that it serves to prevent inadvertent limiting ofthe vertical command, while allowing more aggressive collective decreasefor larger rotor speed decreases. When the difference between commandedrotor speed 401 and actual rotor speed 403 is small, the table output isa large value, which allows a high authority on the vertical speedcommand. As the rotor speed droops closer to the specified limit (inthis case, 3%), the table output decreases, which reduces the authorityof the vertical command. Once rotor speed droops below 3%, the tableoutput is negative, which would result in a decrease in collective. Thevalues in the lower portion of table 405 allow for more aggressivedecrease in collective for larger rotor speed droops due to thenonlinear relationship therebetween. In the example shown, for rotorspeed decreases between 3 and 8%, the value in table 405 decreases from0 to −1.5. When rotor speed decreases below 8%, the table outputdecreases more steeply.

Referring now also to FIG. 5, a method 501 of assisting in rotor speedcontrol in a rotorcraft includes a step 503 of measuring a rotor speedwith a sensor; at step 505 of detecting a droop in the rotor speedbeyond a lower droop limit; and a step 507 of commanding a decrease incollective in response to the rotor speed drooping beyond the lowerdroop limit.

The system and method of the present disclosure successfully transitionsbetween engine throttle governing and collective pitch governing tocontrol rotor speed. The system and method allows collective pitchgoverning in circumstances when rotor speed has dropped beyond athreshold that is well below normal operating ranges. The system andmethod prevents excessive rotor speed droop after a dual engine failure,without requiring engine failure detection. As such, it is robust todelayed engine failure detection and nuisance engine failuredeclarations. A dual engine failure detection is not required forinitial operation, but can be used to improve long term response. Onebenefit of the system of the present disclosure is that it will aid thepilot in an emergency situation, greatly relieving the requirement forimmediate pilot action. It reduces pilot workload after a dual enginefailure.

Referring now also to FIG. 6, a computer system 601 is schematicallyillustrated. Computer system 601 can be configured for performing one ormore functions with regard to the operation of system and method furtherdisclosed herein. Further, any processing and analysis can be partly orfully performed by computer system 601. Computer system 601 can bepartly or fully integrated with other aircraft computer systems.

The system 601 can include an input/output (I/O) interface 603, ananalysis engine 605, and a database 607. Alternative embodiments cancombine or distribute the input/output (I/O) interface 603, analysisengine 605, and database 607, as desired. Embodiments of the system 601can include one or more computers that include one or more processorsand memories configured for performing tasks described herein. This caninclude, for example, a computer having a central processing unit (CPU)and non-volatile memory that stores software instructions forinstructing the CPU to perform at least some of the tasks describedherein. This can also include, for example, two or more computers thatare in communication via a computer network, where one or more of thecomputers include a CPU and non-volatile memory, and one or more of thecomputer's non-volatile memory stores software instructions forinstructing any of the CPU(s) to perform any of the tasks describedherein. Thus, while the exemplary embodiment is described in terms of adiscrete machine, it should be appreciated that this description isnon-limiting, and that the present description applies equally tonumerous other arrangements involving one or more machines performingtasks distributed in any way among the one or more machines. It shouldalso be appreciated that such machines need not be dedicated toperforming tasks described herein, but instead can be multi-purposemachines, for example computer workstations, that are suitable for alsoperforming other tasks.

The I/O interface 603 can provide a communication link between externalusers, systems, and data sources and components of the system 601. TheI/O interface 603 can be configured for allowing one or more users toinput information to the system 601 via any known input device. Examplescan include a keyboard, mouse, touch screen, and/or any other desiredinput device. The I/O interface 603 can be configured for allowing oneor more users to receive information output from the system 601 via anyknown output device. Examples can include a display monitor, a printer,cockpit display, and/or any other desired output device. The I/Ointerface 603 can be configured for allowing other systems tocommunicate with the system 601. For example, the I/O interface 603 canallow one or more remote computer(s) to access information, inputinformation, and/or remotely instruct the system 601 to perform one ormore of the tasks described herein. The I/O interface 603 can beconfigured for allowing communication with one or more remote datasources. For example, the I/O interface 603 can allow one or more remotedata source(s) to access information, input information, and/or remotelyinstruct the system 601 to perform one or more of the tasks describedherein.

The database 607 provides persistent data storage for system 601. Whilethe term “database” is primarily used, a memory or other suitable datastorage arrangement may provide the functionality of the database 607.In alternative embodiments, the database 607 can be integral to orseparate from the system 601 and can operate on one or more computers.The database 607 preferably provides non-volatile data storage for anyinformation suitable to support the operation of system 201 and method501, and various embodiments thereof, including various types of datadiscussed further herein. The analysis engine 605 can include variouscombinations of one or more processors, memories, and softwarecomponents.

The particular embodiments disclosed herein are illustrative only, asthe system and method may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Modifications, additions, or omissionsmay be made to the system described herein without departing from thescope of the invention. The components of the system may be integratedor separated. Moreover, the operations of the system may be performed bymore, fewer, or other components.

Furthermore, no limitations are intended to the details of constructionor design herein shown, other than as described in the claims below. Itis therefore evident that the particular embodiments disclosed above maybe altered or modified and all such variations are considered within thescope and spirit of the disclosure.

To aid the Patent Office, and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims to invokeparagraph 6 of 35 U.S.C. § 112 as it exists on the date of filing hereofunless the words “means for” or “step for” are explicitly used in theparticular claim.

The invention claimed is:
 1. A system for assisting in rotor speedcontrol in a rotorcraft, the system comprising: a sensor configured formeasuring the rotor speed; and a computer having a droop protectionloop, the droop protection loop configured to detect a drop in rotorspeed beyond a droop rotor limit speed, the droop protection loopoperable to generate a decrease collective command to a collectiveactuator in response to a measured rotor speed decreasing below a lowerdroop limit, the droop protection loop operable to generate the decreasein collective command without the detection of an engine failure;wherein the lower droop limit is below a normal lower rotor speed range;and wherein the collective actuator is configured to cause a pitchchange in a rotor blade as a function of the commanded decrease incollective to provide an initial increase in rotor speed.
 2. The systemaccording to claim 1, wherein a magnitude of the decrease collectivecommand has a nonlinear relationship to an amount of the rotor speeddrooping beyond the lower droop limit.
 3. The system according to claim2, wherein the magnitude of the decrease collective commandexponentially increases as the amount of the rotor speed drooping beyondthe lower droop limit increases.
 4. The system according to claim 1,wherein the computer further comprises: a vertical loop configured togenerate a decrease collective command so that the rotorcraft can hold adesired vertical axis state such as vertical speed or vertical altitude.5. The system according to claim 4, further comprising: a selectorconfigured to choose the lesser of the decrease collective commands madeby the vertical loop and the droop protection loop.
 6. The systemaccording to claim 5, further comprising: a controller configured toreceive the decrease collective command and adjust the collectivecommand to minimize an error signal.
 7. The system according to claim 6,wherein the controller is a proportional plus integral controller. 8.The system according to claim 1, wherein the computer is a flightcontrol computer located in the rotorcraft.
 9. The system according toclaim 1, wherein the rotor speed decreasing below the lower droop limitis due to an undetected engine failure.
 10. An aircraft, comprising: arotor blade; a collective actuator for controlling the pitch of therotor blade; and a flight control computer operably associated with thecollective actuator, the flight control computer having a droopprotection loop operable to generate a decrease collective command tothe collective actuator in response to a rotor speed decreasing below alower droop limit, the droop protection loop operable to generate thedecrease in collective command without the detection of an enginefailure; wherein the lower droop limit is below a normal lower rotorspeed range; and wherein the collective actuator is configured to causea pitch change in the rotor blade as a function of the commandeddecrease in collective to provide an initial increase in rotor speed.11. The aircraft according to claim 10, wherein a magnitude of thedecrease collective command has a nonlinear relationship to an amount ofthe rotor speed drooping beyond the lower droop limit.
 12. The aircraftaccording to claim 11, wherein the magnitude of the decrease collectivecommand exponentially increases as the amount of the rotor speeddrooping beyond the lower droop limit increases.
 13. The aircraftaccording to claim 10, wherein the flight control computer furthercomprises: a vertical loop configured to generate a decrease collectivecommand so that the rotorcraft can hold a desired vertical axis statesuch as vertical speed or vertical altitude.
 14. The aircraft accordingto claim 13, further comprising: a selector configured to choose thelesser of the decrease collective commands made by the vertical loop andthe droop protection loop.
 15. The aircraft according to claim 14,further comprising: a controller configured to receive the decreasecollective command and adjust the decrease collective command tominimize an error signal.
 16. The aircraft according to claim 15,wherein the controller is a proportional plus integral controller. 17.The aircraft according to claim 10, wherein the lower droop limit is afunction of a difference between a commanded rotor speed and the rotorspeed.